1. Field of the Invention
The present invention relates generally to sealing gaskets and sealing systems used for pipe joints in plastic pipelines in which a male spigot pipe section is installed within a mating female socket pipe section to form a pipe joint and, more specifically, to an improved gasket, simplified method of manufacture, as well as an installation method for installing a locked-in gasket within a preformed gasket groove in a section of pipe used to form a pipe joint.
2. Description of the Prior Art
Fluid sealing systems for plastic, fluid conveying pipes are used in a variety of industries. The pipes used in such systems are typically formed from thermoplastic materials including polyolefins and PVC. In forming a joint between sections of pipe, the spigot or male pipe end is inserted within the female or socket pipe end. An annular, elastomeric ring or gasket is typically seated within a groove formed in the socket end of the thermoplastic pipe. As the spigot is inserted within the socket, the gasket provides the major seal capacity for the joint. Various types of sealing technologies have been employed to assure the sealing integrity of the pipe joint. It is important that the sealing gasket not be dislodged during the joint make up and that the gasket not become twisted or otherwise compromised in field applications. It is also important that the gasket not extrude out of the pipe groove under various pressure conditions.
Earlier gasketed sealing systems are known in which a homogeneous rubber gasket was generally deformable, allowing it to be flexed, or bent by hand, accepting inverse curvature, and inserted within a mating internal raceway formed in the female, belled pipe end. The raceway in the female pipe bell end was pre-formed using a collapsible mandrel belling tool at the pipe manufacturing facility. A prior art attempt to insure the integrity of such pipe joints involved the use of a pipe gasket having a first distinct body region formed of an elastically yieldable sealing material, such as rubber, bonded to a second distinct body region formed of a more rigid material, such as a rigid plastic. The intent was that the rigid body region of the gasket would assist in holding the gasket in place within the pipe groove. Other approaches to the problem included the use of a homogeneous rubber ring with a stiffening band which was inserted into a mating groove provided on the internal diameter of the rubber ring. In the other prior art systems, a homogeneous rubber gasket body was bonded with an internal or external metal, or plastic, reinforcing band or an internal metal band or ring. Each of these solutions had critical limitations. For example, the prior art plastic/rubber composites sometimes allowed the infiltration of dirt and debris between the bell raceway and the outer diameter of the gasket. The plastic region in some cases, reduced the rubber surface contact area, sometimes leading to problems in providing the needed sealing in all conditions, including high pressure, low pressure and cyclic surges. Compatible materials were necessary when bonding the homogeneous rubber gasket body with the plastic reinforcing band. Poor bonding resulted in separation of the two elements. The reinforcing band was subject to being misplaced and breakage in the two part system. Thus, in some cases, the prior art solutions failed to provide the needed joint integrity, often contributing to the complexity and expense of the manufacturing operation and field installation.
In the early 1970's, a new technology was developed by Rieber & Son of Bergen, Norway, referred to in the industry as the “Rieber Joint.” The Rieber system employed a combined mould element and sealing ring for sealing a joint between the socket end and spigot end of two cooperating pipes formed from thermoplastic materials. In the Richer process, an elastomeric gasket was installed within an internal groove in the socket end of the female pipe as the female or belled end was simultaneously being formed. Rather than utilizing a preformed groove, the Rieber process provided a prestressed and anchored elastomeric gasket during the belling operation. Because the gasket was installed simultaneously with the formation of the belled pipe end, a rigid, embedded reinforcing ring could be supplied as a part of the gasket. Because the pipe groove was, in a sense, formed around the gasket with its embedded reinforcing ring, the gasket was securely retained in position and did not tend to twist or flip or otherwise allow impurities to enter the sealing zones of the joint, thus increasing the reliability of the joint and decreasing the risk of leaks or possible failure due to abrasion. The Richer process is described in the following issued United States patents, among others: U.S. Pat. Nos. 4,120,521; 4,061,459; 4,030,872; 3,965,715; 3,929,958; 3,887,992; 3,884,612; and 3,776,682.
Despite the advances offered by the Richer process, the belling operation was somewhat complicated and costly. Also, certain situations exist in which it would be desirable to manually remove one gasket and reinstall another within a preformed raceway in the selected pipe end, rather than utilizing an integrally installed gasket in which the groove in the pipe is formed around the gasket. For example, municipal and consulting engineers will specify specialty elastomers based on the pipelines end-use and soil conditions. While SBR is the most common rubber used in North America, engineers will specify EPDM based on water treatment technique, and nitrile rubber when there is hydrocarbon soil contamination due to gasoline or oil pollution. Distributors and contractors cannot exchange Rieber process gaskets in their pipe inventory.
It would therefore be advantageous to be able to install a gasket of the type having a reinforcing element within a previously belled pipe end, as opposed to those systems like the Richer systems, where the female pipe end is formed about the sealing gasket during the manufacture of the female pipe end. However, prior art gaskets with reinforcing elements are subject to breakage and are not easily bent or flexed by hand, thus generally precluding hand assembly in the field. The size and position of the reinforcing element, which is bonded to the gasket body, generally was greater than the diameter of the mouth opening of the belled pipe end, presenting a further complication for assembly.
U.S. Pat. No. 6,044,539, issued Apr. 4, 2000, to Guzowski, and commonly owned by the present applicant describes a machine for inserting a “snap-fit” gasket, unable to accept inverse curvature, having an embedded reinforcing ring into a preformed gasket receiving groove in a belled pipe end. However, such a machine was fairly costly to construct and presented difficulties in being hand carried by a worker in the field.
The present invention has, as one object, to provide an improved pipe gasket for use in pipe joints which offers the advantage of a Rieber type seal, while allowing the gasket to accept inverse curvature, to be installed in a preformed groove by hand, either at the manufacturing plant or in a field operation.
Another object of the invention is to provide an improved gasket which is securely retained within a preformed pipe groove without the necessity of a separate retaining band.
Another object of the invention is to provide an improved sealing gasket of the plastic/rubber variety which optimizes the rubber sealing surface contact of the gasket with the pipe bell raceway.
Another object of the invention is to provide a reinforcing element that is not required to be bonded to the rubber element, hence creating the possibility of being made from a multitude of materials.
Another object of the invention is to provide such a sealing gasket with special reinforcing attributes which allow it to seal under a variety of pressure conditions without being twisted or extruded, or displaced during field assembly, and yet which can be installed by hand in the bell raceway.